WO2022185778A1

WO2022185778A1 - Aluminum substrate for collector, capacitor, secondary cell, and method for manufacturing aluminum substrate for collector

Info

Publication number: WO2022185778A1
Application number: PCT/JP2022/002429
Authority: WO
Inventors: 宏和澤田; 浩之野田; 泰弘川谷
Original assignee: 富士フイルム株式会社
Priority date: 2021-03-02
Filing date: 2022-01-24
Publication date: 2022-09-09
Also published as: JPWO2022185778A1; TW202235635A; CN116940717A

Abstract

Provided are: an aluminum substrate for a collector having a high adhesion performance with respect to an electrode material and a low contact resistance with an electrode material; a capacitor; a secondary cell; and a method for manufacturing the aluminum substrate for a collector. The present invention has a face in which (C + D)/(A + B + C + D) is 0.5 to 1 inclusive and C/D is 0.1 to 2 inclusive, where A, B, C, and D respectively represent the peak area ratios of Al, Al2O3, Al(OH)3, and AlO(OH) present within 10 nm of the surface layer when measured by X-ray photoelectron spectroscopy.

Description

Aluminum substrate for current collector, capacitor, secondary battery, and method for producing aluminum substrate for current collector

The present invention relates to an aluminum base material for current collector, a capacitor and a secondary battery using this aluminum base material for current collector, and a method for producing the aluminum base material for current collector.

In recent years, with the development of portable equipment such as personal computers and mobile phones, hybrid automobiles, electric automobiles, etc., there is a demand for power storage devices, especially lithium ion capacitors, lithium ion secondary batteries, electric double layer capacitors, etc. is increasing.

It is known that an aluminum base material can be used as an electrode current collector (hereinafter simply referred to as "current collector") used for the positive electrode and/or negative electrode of such an electricity storage device. It is also known that an active material, activated carbon, or the like as an electrode material can be applied to the surface of a current collector made of an aluminum base material, and used as a positive electrode or a negative electrode.

For example, in Patent Document 1, an aluminum substrate and an oxide film laminated on at least one main surface of the aluminum substrate are provided, and the oxide film has a density of 2.7 to 4.1 g/cm ³ . , an aluminum member for an electrode having a thickness of 5 nm or less.

Patent Document 2 discloses a conductive material comprising a positive electrode current collector, a positive electrode mixture layer, and an intermediate layer provided between the positive electrode current collector and the positive electrode mixture layer, wherein the intermediate layer is a non-oxide conductive material. a first intermediate layer containing a conductive inorganic compound and a positive electrode active material; and a second intermediate layer containing an insulating inorganic material and a non-oxide conductive inorganic compound, wherein the conductive inorganic compound contains 300 A positive electrode for a secondary battery is described which becomes an insulating oxide at ℃ or higher.

WO2018/062046 WO2018/220991

It is desirable that the current collector has high adhesion to the electrode material and low contact resistance with the electrode material. Although it is possible to improve the adhesion to the electrode material by roughening the surface of the aluminum base material, it has been difficult to achieve both a sufficient adhesion effect and a reduction in contact resistance. In addition, sufficient effect was not obtained with respect to the cost of surface roughening treatment, and it was almost never put into practical use.

In addition, since the surface of commercially available aluminum foil for current collectors has a natural oxide film formed during the rolling process and a small amount of rolling oil, there are problems with contact resistance and adhesion with electrode materials.

The present invention provides an aluminum base material for a current collector, a capacitor, a secondary battery, and a method for producing an aluminum base material for a current collector, which have high adhesion to an electrode material and low contact resistance with the electrode material. The task is to provide

The present invention solves the problem with the following configuration.

[1] The peak area ratios of metals Al, Al ₂ O ₃ , Al(OH) ₃ and AlO(OH) existing within 10 nm of the surface layer when measured by X-ray photoelectron spectroscopy are indicated by A, B, and C in that order. , and D, (C+D)/(A+B+C+D) is 0.5 or more and 1 or less, and C/D is 0.1 or more and 2 or less.
[2] The aluminum substrate for a current collector according to [1], wherein the surface roughness Ra of the surface is 10 nm or more and 50 nm or less.
[3] The aluminum base material for a current collector according to [1] or [2], wherein the maximum surface height difference PV is 100 nm or more and 500 nm or less.
[4] The aluminum substrate for a current collector according to any one of [1] to [3], which has a granular intermetallic compound on the surface.
[5] The aluminum substrate for a current collector according to [4], wherein the number density of the granular metal compounds is 500/mm ² or more.
[6] The aluminum substrate for current collector according to any one of [1] to [5], which has a thickness of 5 μm to 100 μm.
[7] A capacitor comprising the aluminum substrate for current collector according to any one of [1] to [6].
[8] A secondary battery comprising the aluminum substrate for current collector according to any one of [1] to [6].
[9] A method for producing an aluminum substrate for a current collector for producing the aluminum substrate for a current collector according to any one of [1] to [6], comprising:
a film-forming step of forming an anodized film on the surface of the aluminum foil at a current of 10 to 100 C/dm ² during anodic electrolysis;
A method for producing an aluminum base material for a current collector, comprising a removing step of removing the anodized film.
[10] The method for producing an aluminum base material for current collector according to [9], wherein the removing step includes, in this order, a chemical etching step with an alkaline solution, a water washing step, a washing step with an acid solution, and a water washing step.
[11] The method for producing an aluminum substrate for a current collector according to [10], wherein the chemical etching step includes a step of contacting the anodized film with an alkaline solution at 25°C or higher and lower than 50°C for 1 second to 10 seconds.

INDUSTRIAL APPLICABILITY According to the present invention, production of an aluminum base material for a current collector, a capacitor, a secondary battery, and an aluminum base material for a current collector having high adhesion to an electrode material and low contact resistance with the electrode material. can provide a method.

BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum base material for collectors of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum base material for collectors of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum base material for collectors of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum base material for collectors of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is typical sectional drawing for demonstrating an example of the suitable manufacturing method of the aluminum base material for collectors of this invention. 6 is an enlarged view of region R1 in FIG. 5; FIG. FIG. 7 is an enlarged view of region R2 in FIG. 6; BRIEF DESCRIPTION OF THE DRAWINGS It is a conceptual diagram which shows an example of the manufacturing apparatus which enforces the manufacturing method of the aluminum base material for current collectors of this invention. It is a figure which shows typically the apparatus which measures resistance. 1 is an SEM image of an aluminum substrate for a current collector of an example. It is a SEM image of the aluminum base material for current collectors of a comparative example. It is a SEM image of the aluminum base material for current collectors of a comparative example. It is a figure which shows typically the measuring apparatus which measures peel strength.

The present invention will be described in detail below.
The description of the constituent elements described below may be made based on representative embodiments of the present invention, but the present invention is not limited to such embodiments.
In this specification, a numerical range represented by "-" means a range including the numerical values before and after "-" as lower and upper limits.

[Aluminum base material for current collector]
The aluminum base material for a current collector of the present invention is
A, B, C, and D represent peak area ratios of metal Al, _Al2O3 , Al(OH) ₃ _, and AlO(OH) present within 10 nm of the surface layer when measured by X-ray photoelectron spectroscopy. (C+D)/(A+B+C+D) is 0.5 or more and 1 or less, and C/D is 0.1 or more and 2 or less.

The structure of the aluminum base material for current collector of the present invention will be described.

The aluminum base material for a current collector of the present invention contains metal Al, Al ₂ O ₃ , Al(OH) ₃ , AlO present within 10 nm of the surface layer when measured by X-ray photoelectron spectroscopy (hereinafter also referred to as XPS). When the peak area ratios of (OH) are A, B, C, and D in order, (C + D) / (A + B + C + D) is 0.5 or more and 1 or less, and C/D is 0.1 or more and 2 or less has a configuration that has a surface that is

That is, the aluminum substrate for a current collector of the present invention has, on at least one surface, two kinds of hydroxides, aluminum hydroxide Al(OH) ₃ and aluminum oxide hydrate, in the surface layer of the aluminum substrate. (boehmite) and AlO(OH) at a certain level or more, and among the hydroxides, aluminum hydroxide Al(OH) ₃ at a certain level or more.

The aluminum substrate for a current collector of the present invention is used as a current collector, and an active material (electrode material) is applied to the surface to be used as a positive electrode or a negative electrode of an electric storage device or the like.

As described above, the current collector is desired to have high adhesion to the electrode material and low contact resistance with the electrode material. Therefore, various configurations have been proposed for the aluminum base material for current collector in order to improve the adhesion with the electrode material and reduce the contact resistance with the electrode material.

For example, by forming a rough surface on the surface of the aluminum base material, it has been proposed to improve the adhesion with the electrode material and improve the resistance. However, even if the surface of the aluminum substrate is roughened in order to improve the adhesion to the electrode material, a sufficient adhesion effect cannot be obtained, and both adhesion and low resistance cannot be satisfactorily achieved. . Further, roughening the surface of the aluminum base material has the drawback of complicating the manufacturing process and increasing the manufacturing cost.

In addition, it has been proposed to improve adhesion by forming an anodized film with fine pores on the surface of the aluminum substrate. However, since the anodized film has poor conductivity, the contact resistance with the electrode material increases when the anodized film is formed on the surface, and it is impossible to achieve both adhesion and low resistance.

Another known method is to form a conductive coating film containing carbon or other conductive particles on an aluminum substrate. It is known that this conductive coating film has fine irregularities formed on the surface by the conductive particles contained in the coating film, so that the adhesion with the electrode material provided thereon is improved and the difficulty of peeling off can be improved. It is However, the configuration in which the conductive coating film is applied in advance has the drawback that the manufacturing process is complicated and the manufacturing cost is increased.

Further, the aluminum substrate usually has a natural oxide film formed on its surface, and the natural oxide film contains Al ₂ O ₃ and its hydrate Al ₂ O ₃ ·nH ₂ O. Since the natural oxide film itself is a material with poor conductivity, it is possible to reduce the contact resistance with the electrode material by making it thinner or by stipulating the density of the oxide film. It is also known to be possible.

However, according to the studies of the present inventors, there are cases where the adhesion with the electrode material and the contact resistance with the electrode material are not sufficiently improved only by controlling the thickness and density of the natural oxide film. I found something.

On the other hand, the aluminum substrate for a current collector of the present invention contains metal Al, Al ₂ O ₃ , Al ( OH) ₃ and AlO(OH) where the peak area ratios are A, B, C, and D in that order, (C+D)/(A+B+C+D) is 0.5 or more and 1 or less, and C/D is 0 .1 or more and 2 or less faces.

According to the studies of the present inventors, it was found that the hydroxide near the surface layer of the aluminum base material affects the interfacial resistance in addition to the thickness of the natural oxide film. Specifically, there are two kinds of hydroxides, AlO(OH) and Al(OH) ₃ , as hydroxides existing near the surface layer of the aluminum base material, and AlO(OH) (boehmite) adversely affects the interfacial resistance. and that even if AlO(OH) is present, the low resistance can be maintained if another hydroxide, Al(OH) ₃ , is present to some extent. Therefore, it has been found that a low resistance can be achieved by keeping the ratio of Al(OH) ₃ in these two kinds of hydroxides within 10 nm of the surface layer at a certain level or higher. Specifically, the peak area ratio Al(OH) ₃ /AlO(OH) of hydroxide present within 10 nm of the outermost layer is 0.1 or more, which is essential for achieving low resistance. If the peak area ratio is 2 or less, the adhesion at the time of joining is good, so the upper limit of the peak area ratio is set to 2.

In addition, as will be described in detail later, the aluminum substrate for current collector having the hydroxide in the above ratio on the surface layer is formed with an anodized film under appropriate conditions, and then the anodized film is removed under appropriate conditions. It is made by At that time, fine unevenness is formed on the surface of the aluminum substrate due to the influence of fine unevenness having a diameter of about several 10 nm formed on the bottom of the anodized film. Therefore, it turned out that adhesiveness can also be improved.

The aluminum base material for a current collector of the present invention, which has low contact resistance with electrode materials and high adhesion with electrode materials, can be used in secondary batteries such as lithium ion batteries and power storage devices such as capacitors. In addition to contributing to the reduction of internal resistance, partial separation between the electrode material and the current collector can be suppressed even when charging and discharging are performed many times over a long period of time. In particular, among lithium-ion batteries, the effect is exhibited in all-solid batteries and semi-solid batteries that require close contact and low resistance such as solid or semi-solid electrolytes.

Here, a method for measuring the peak area ratios A, B, C, and D of metal Al, Al ₂ O ₃ , Al(OH) ₃ , and AlO(OH) existing within 10 nm of the surface layer will be described.

"X-ray photoelectron spectroscopy" is an analysis method commonly called ESCA (Electron Spectroscopy for Chemical Analysis) or XPS (X-ray Photoelectron Spectroscopy). In the following, X-ray photoelectron spectroscopy is also referred to as XPS. XPS is an analysis method that utilizes the fact that photoelectrons are emitted when the surface of a sample to be measured is irradiated with X-rays, and is widely used as a method for analyzing the surface layer of the sample to be measured. According to XPS, qualitative analysis and quantitative analysis can be performed using an X-ray photoelectron spectroscopy spectrum obtained by analysis on the surface of a sample to be measured. Between the depth from the sample surface to the analysis position (hereinafter also referred to as “detection depth”) and the photoelectron take-off angle, the following formula generally holds: detection depth≈electron mean freedom A formula of stroke×3×sin θ is established. In the formula, the detection depth is the depth at which 95% of the photoelectrons forming the X-ray photoelectron spectroscopy spectrum are generated, and θ is the photoelectron extraction angle. From the above formula, it can be seen that the smaller the photoelectron take-off angle, the shallower the sample surface can be analyzed, and the larger the photoelectron take-off angle, the deeper the sample can be analyzed. In the analysis performed by XPS at a photoelectron take-off angle of 45 degrees, the analysis position is usually a very superficial layer at a depth of about 10 nm from the sample surface. Therefore, according to the analysis performed by XPS on the surface of the aluminum base material for current collector at a photoelectron take-off angle of 45 degrees, the composition analysis of the very surface layer at a depth of about 10 nm from the surface of the aluminum base material for current collector can be performed. It can be carried out.

For the Al2p spectrum obtained by XPS, peak shift correction was performed for each of Al ₂ O ₃ , Al(OH) ₃ , and AlO(OH) based on the peak position of metallic Al, and then background correction was performed on the data. By fitting peak heights to fixed peak positions and peak widths, peaks corresponding to Al, Al ₂ O ₃ , Al(OH) ₃ , and AlO(OH) are obtained. Peak area ratios A, B, C, and D are obtained from each peak.

As an XPS measuring device, for example, a commercially available measuring device such as Quantera SXM manufactured by Ulvac-PHI can be used. Moreover, the measurement conditions may be set as follows, for example.
・X-ray source: Al Kα ray (1486.6 ev, 25 W, 15 kV)
・Pass Energy = 55 ev, Step = 0.05 ev
・Measurement area: 300 μm × 300 μm
・Photoelectron extraction angle: 45 degrees

Here, (C+D)/(A+B+C+D) is preferably 0.55 or more and 1 or less, more preferably 0.6 or more and 0.7 or less, from the viewpoint of achieving both adhesion with the electrode material and low resistance. Similarly, C/D is preferably 0.12 or more and 2 or less, more preferably 0.15 or more and 1 or less.

Here, from the viewpoint of achieving both adhesion with the electrode material and low resistance, metals Al, Al ₂ O ₃ , Al(OH) ₃ , AlO(OH) existing within a surface layer of 5 nm measured by X-ray photoelectron spectroscopy. are, in order, A ₂ , B ₂ , C ₂ , and D ₂ , where (C ₂ +D ₂ )/(A ₂ +B ₂ +C ₂ +D ₂ ) is 0.5 or more and 1 or less, In addition, C ₂ /D ₂ is preferably 0.4 or more and 1 or less. ( _C2 +D2)/( _A2 +B2 ₊ _C2 ₊ D2) is _more preferably 0.6 or more and 1 or less, and more preferably 0.65 or more and 0.7 or less. Similarly, C ₂ /D ₂ is more preferably 0.5 or more and 2 or less, and more preferably 0.7 or more and 1 or less.

In addition, in the case of performing composition analysis of the surface layer portion at a depth of 5 nm from the surface of the aluminum substrate for current collector, the photoelectron extraction angle may be set to 20 degrees in the above XPS measurement.

Further, from the viewpoint of achieving both adhesion to the electrode material and low resistance, the surface roughness Ra of the surface of the aluminum substrate for current collector that satisfies the above-described peak area ratio is preferably 10 nm or more and 50 nm or less, and 11 nm or more. 40 nm or less is more preferable, and 11 nm or more and 36 nm or less is even more preferable.

In addition, from the viewpoint of achieving both adhesion with the electrode material and low resistance, the maximum height difference PV of the surface satisfying the above-described peak area ratio of the aluminum base material for current collector is 100 nm or more and 500 nm or less. It is preferably 120 nm or more and 200 nm or less, and even more preferably 120 nm or more and 160 nm or less.

The surface roughness Ra and the maximum height difference PV are measured as follows.

Using an atomic force microscope (AFM), the surface shape of a 1 μm square of the aluminum substrate is measured, and from the obtained three-dimensional data, the surface roughness Ra and the maximum height difference P- Calculate V respectively.
· Average surface roughness Ra (nm) = 1/n × Σ|Z (i) - Zc| (Zc is the Z coordinate of the center plane (height direction))
・Maximum height difference PV (nm) = maximum value of Z coordinate in measurement plane - minimum value

As an atomic force microscope (AFM), for example, AFM5100N type SPM manufactured by Hitachi High-Tech Science Co., Ltd. can be used. Using this apparatus in the tapping mode, OMCL-AC200TS-R3 manufactured by Olympus Corporation is used as a cantilever, and three-dimensional data of the surface of the aluminum substrate is measured at a resolution of 256×256 pixels.
By subjecting the obtained data to FFT (Fast Fourier Transform) processing, for example, three-dimensional data with a period of 0.2 μm or more can be removed, and the surface roughness and maximum height difference P- V can be calculated.
Here, the three-dimensional data subjected to FFT processing means that the shape image obtained by performing fast Fourier transform (FFT) processing on the obtained data is converted into wavenumber space, subjected to high-pass filtering, and then reversed. The shape image is reconstructed by Fourier transform (FFT) processing. By performing high-pass filter processing, a large wave component originating from the aluminum foil having a wavelength of 0.2 μm or more is removed.
Except for three-dimensional data with a period of 0.2 μm or more, the surface roughness Ra reflecting short-period unevenness is preferably 5 nm or more and 10 nm or less, and 6 nm, from the viewpoint of achieving both adhesion with the electrode material and low resistance. 10 nm or less is more preferable, and 6 nm or more and 9 nm or less is even more preferable.
Similarly, except for three-dimensional data with an F period of 0.2 μm or more, the maximum height difference PV reflecting short-period unevenness is preferably 50 nm or more and 200 nm or less, and 60 nm or more and 100 nm or less. is more preferable, and more preferably 70 nm or more and 100 nm or less.

Further, the thickness of the aluminum substrate for current collector is preferably 5 μm to 100 μm, more preferably 10 μm to 30 μm. If the thickness of the aluminum substrate for current collector is too thin, there is a risk of breakage. On the other hand, the thickness of the current collector aluminum base material is preferably 100 μm or less in order to reduce the overall thickness when used in an electricity storage device or the like.

The aluminum substrate for a current collector of the present invention may have through-holes penetrating in the thickness direction of the aluminum substrate.

The aluminum base material for current collector has a plurality of through-holes penetrating in the thickness direction, so that when used as a current collector, the movement of charged particles can be facilitated. In addition, by having a large number of through holes, it is possible to improve the adhesion with the active material.

The average opening diameter of the through-holes is preferably 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 80 μm or less, even more preferably 3 μm or more and 40 μm or less, and particularly preferably 5 μm or more and 30 μm or less.

By setting the average opening diameter of the through-holes within the above range, it is possible to prevent the occurrence of omissions when the active material or the like is applied to the aluminum base material for the current collector, and the adhesiveness to the applied active material is improved. can be improved. Moreover, even when the aluminum base material for current collector has a large number of through-holes, it can have sufficient tensile strength.

In addition, the average opening diameter of the through-holes is measured as follows.
Parallel light is irradiated from one surface of the aluminum substrate for current collector, and the through-hole is photographed with a transmission optical microscope at a magnification of 200 times. The obtained data is binarized by image analysis software, and the average value of the circle-equivalent diameters of the through-holes is taken as the average opening diameter.

Further, the average opening ratio of the through holes is preferably 0.5% to 30%, more preferably 0.6% to 20%, still more preferably 0.7% to 10%, and 0.8% to 5% is particularly preferred.

By setting the average aperture ratio of the through-holes within the above range, it is possible to prevent the occurrence of voids when the active material is applied to the aluminum base material for current collector, and also to improve the adhesion with the applied active material. can improve. Moreover, even when the aluminum base material for current collector has a large number of through-holes, it can have sufficient tensile strength.

The average aperture ratio of through holes is measured as follows.
Parallel light is irradiated from one surface of the aluminum substrate for current collector, and the through-hole is photographed with a transmission optical microscope at a magnification of 200 times. The obtained data is binarized by image analysis software, and calculated as the total area of the openings/observed area×100(%).

Here, in the present invention, it is preferable that the aluminum substrate for current collector has a large number of granular intermetallic compounds dispersed in the film on its surface. In the following description, the granular intermetallic compound is also simply referred to as "intermetallic compound".

　Aluminum oxide has a higher resistance than aluminum metal alone. On the other hand, if the aluminum base material contains an intermetallic compound, the aluminum oxide also contains the intermetallic compound, which lowers the insulating properties.

The intermetallic compound preferably has an element ratio O/Al of oxygen to aluminum of 2 or more and 4 or less. Also, the number density of the granular intermetallic compounds is preferably 500/mm ² or more.

Here, the intermetallic compound in the present invention is a compound containing aluminum element (Al) and at least one selected from Fe, Si, Mn, Mg, Ti, B and the like. Specifically, the intermetallic compounds include Al ₃ Fe, Al ₆ Fe, αAlFeSi, and AlFeMnSi. Since it contains Al, an aluminum oxide film is formed on the surface. Therefore, the surface layer of the intermetallic compound in the present invention contains an oxygen element (O).

The aluminum base material for a current collector of the present invention contains granular intermetallic compounds having an oxide film having an element ratio O/Al of 2 or more and 4 or less on the surface layer at a density of 500/mm ² or more. If it has, it may have other granular intermetallic compounds. That is, the oxide film on the surface layer may have a granular intermetallic compound with an element ratio O/Al of less than 2 or more than 4.

Further, when the oxide film contains aluminum oxide (Al ₂ O ₃ ) as a main component and does not contain a hydrate, the element ratio O/Al in the portion other than the intermetallic compound of the oxide film is preferably less than 2. , about 1.3 to 1.5.

From the viewpoint of lowering the electric resistance of the aluminum base material for current collector, the average value of the element ratio O/Al of the oxide film on the surface layer of the intermetallic compound is preferably 2 or more and 4 or less. More preferably, it is 5 or more and 3.5 or less.

The element ratio O/Al of the surface layer of the intermetallic compound is measured as follows.

When observing the surface of the oxide film with a high-resolution scanning electron microscope (SEM), the intermetallic compound can be visually distinguished from the portion of the oxide film other than the intermetallic compound. Therefore, first, the surface of the oxide film is photographed using a high-resolution scanning electron microscope (SEM) at a magnification of, for example, 5000 times, and the position of the intermetallic compound is identified in the obtained SEM photograph. Next, elemental analysis is performed using field emission Auger electron spectroscopy (FE-AES) in the depth direction from the outermost surface at the position of the extracted intermetallic compound. Depth analysis is performed by repeating the measurement and surface removal by sputtering. From the result of the element distribution in the depth direction by FE-AES, the element ratio O/Al in the outermost layer is obtained.

The number density of the granular intermetallic compound is preferably 1,000/mm ² to 300,000/mm ² , more preferably 5,000/mm ² to 200,000 from the viewpoint of lowering the electric resistance of the aluminum substrate for current collector. pcs/mm ² is more preferred.

The number density of granular intermetallic compounds is measured as follows.

First, using a high-resolution scanning electron microscope (SEM), the surface of the aluminum base material for current collector is photographed from directly above at a magnification of, for example, 5000 times to extract granular intermetallic compounds. Next, the elemental ratio O/Al of each intermetallic compound extracted by elemental analysis using FE-AES is obtained. Count the number of granular intermetallic compounds having an element ratio O/Al of 2 or more and 4 or less, and calculate the number density from the number of granular intermetallic compounds in the field of view and the area of the field of view (geometric area). do. When using a plurality of SEM photographs, the average value of the number density of each photograph is calculated as the density.

Here, the equivalent circle diameter of the granular intermetallic compound is preferably 1 μm or less. An intermetallic compound having an equivalent circle diameter of 1 μm or less is likely to appear on the surface of the aluminum substrate for current collector. When a small intermetallic compound appears on the surface of the aluminum base material for current collector, the surface area to volume of the intermetallic compound increases. As a result, it is considered that water molecules are easily adsorbed locally, and the element ratio O/Al of the oxidized intermetallic compound tends to be 2 or more. As a result, since the oxide film of the intermetallic compound becomes a hydrate, the insulating property becomes lower than that of the surrounding aluminum oxide, which becomes a starting point for lowering the resistance.

The equivalent circle diameter of the granular intermetallic compound is obtained by extracting at least 20 intermetallic compounds whose element ratio O/Al is measured as described above, and using image analysis software or the like to determine the area of the intermetallic compound on the oxide film surface. , the equivalent circle diameter is obtained from this area, and the average value of these values is calculated as the equivalent circle diameter.

The shape of the aluminum substrate for current collector is not particularly limited as long as it can be used as a current collector, but it is preferably plate-like.

<Aluminum substrate>
There is no particular limitation on the aluminum base material that is the base material of the aluminum base material for current collector, and for example, known aluminum base materials such as alloy numbers 1N30, 3003, and 1085 described in JIS H4000 can be used. can be done. The use of aluminum containing a large amount of intermetallic compounds can be expected to have the aforementioned effect of reducing electrical resistance. However, the present application is not limited to the aluminum material. The aluminum base material is an alloy plate containing aluminum as a main component and a small amount of foreign elements.

[Method for producing aluminum substrate for current collector]
Next, the method for producing the aluminum base material for current collector of the present invention will be described.

A method for producing an aluminum substrate for a current collector for producing the aluminum substrate for a current collector of the present invention comprises:
a film-forming step of forming an anodized film on the surface of the aluminum foil at a current of 10 to 100 C/dm ² during anodic electrolysis;
A method for producing an aluminum substrate for a current collector, comprising a removing step of removing the anodized film after the film forming step.

In addition, in the method for producing an aluminum base material for a current collector, the removal of the anodized film in the removal step is preferably performed in the order of chemical etching with an alkaline solution, washing with water, washing with an acidic solution, and washing with water.

In addition, the method for manufacturing an aluminum substrate for a current collector may have a through-hole forming step of forming through-holes penetrating through the aluminum substrate. Moreover, the method for producing an aluminum base material for a current collector may include a roughening step of roughening the surface of the aluminum base material. The through-hole forming step and/or surface roughening step may be performed simultaneously or sequentially with the film forming step of forming the anodized film.

Hereinafter, each step of the method for producing an aluminum base material for a current collector will be described with reference to FIGS. do.

1 to 5 are schematic cross-sectional views for explaining an example of a preferred embodiment of the method for producing an aluminum substrate for a current collector.
As shown in FIGS. 1 to 5, one example of a method for producing an aluminum base material for a current collector is to perform electrolytic treatment on at least one main surface of an aluminum base material 1 having a natural oxide film 2, thereby naturally oxidizing. A film forming step (FIGS. 1 and 2) for forming the anodized film 3 between the film 2 and the aluminum substrate 1, and a removal step ( 2 to 5). Although not shown, the aluminum base material 1 subjected to the film forming process may have rolling oil or the like on the natural oxide film 2 in some cases.

The removal step includes a step of removing the anodized film 3 and the natural oxide film 2 by chemical etching with an alkaline solution (FIGS. 2 and 3, also called chemical etching step), and a step of washing with water after the chemical etching step (also called water washing step). ), a step of removing the residue 5 (see FIG. 4) generated on the surface due to the chemical etching step by washing with an acid solution (FIGS. 4 and 5, also called a pickling step), and a pickling step. and a step of washing with water later (also referred to as a washing step). Aluminum hydroxide is deposited on the surface of the aluminum base material by the chemical etching process and the water washing process (see FIG. 4).

[Coating process]
The film forming step is a step of forming an anodized film on the surface of the aluminum base material. Since the anodized film is formed by changing the metal aluminum, when the surface of the aluminum base material has a natural oxide film, the anodized film is formed between the natural oxide film and the aluminum base material. . Therefore, it is less likely to be affected by the natural oxide film, rolling oil, etc. in the removal process described later.

As for the anodizing treatment method for forming the anodized film, the same treatment as the conventionally known anodizing treatment can be applied. For the anodizing treatment, for example, the conditions and apparatus described in paragraphs [0063] to [0073] of JP-A-2012-216513 can be appropriately employed.

In the present invention, the conditions for the anodizing treatment vary depending on the electrolyte used and cannot be determined indiscriminately. °C, a current density of 0.5 to 60 A/dm ² , a voltage of 1 to 100 V, and an electrolysis time of 1 second to 20 minutes.

In the present invention, it is preferable to perform the anodizing treatment using an aqueous solution containing nitric acid and sulfuric acid. Also, the amount of current applied during anode electrolysis is 10 C/dm ² to 100 C/dm ² , more preferably 30 C/dm ² to 100 C/dm ² , still more preferably 50 C/dm ² to 100 C/dm ² . A thin anodized film is formed at this amount of energization. In the production method of the present invention, a thin anodized film is formed on an aluminum base material, and a removal step (chemical etching step), which will be described later, is performed in a short time, thereby suppressing dissolution of the metal aluminum portion and AlO(OH). ), it is possible to produce an aluminum substrate for a current collector in which the proportion of hydroxide in the surface layer is within a predetermined range.

In addition, in the anodizing treatment, a direct current may be applied between the aluminum substrate and the counter electrode, or an alternating current may be applied. When direct current is applied to the aluminum substrate, the current density is preferably 0.5 to 60 A/dm ² , more preferably 1 to 40 A/dm ² . When the anodizing treatment is continuously performed, it is preferable to perform the anodizing treatment by a liquid feeding method in which the aluminum base material is fed with an electrolytic solution.

[Through hole forming step]
The through-hole forming step is a step of forming through-holes in the aluminum base material.
The method of forming the through-holes in the through-hole forming step is not particularly limited, and mechanical methods such as punching or electrochemical methods such as electrolytic dissolution can be used. A method of forming through-holes by electrolytic dissolution treatment is preferable in that through-holes having an average opening diameter of 0.1 μm or more and less than 100 μm can be easily formed.
Formation of through-holes by electrolytic dissolution treatment can be carried out simultaneously with or sequentially with anodizing treatment in the film forming step.

The electrolytic dissolution treatment is not particularly limited, and for example, the method described in paragraphs [0025] to [0032] of Japanese Patent No. 6199416 can be used.

[Roughening process]
In the roughening step, the aluminum substrate is subjected to electrochemical graining treatment (hereinafter also abbreviated as "electrolytic graining treatment") to roughen the surface and/or the back surface of the aluminum substrate. It is a process.
By roughening the surface of the aluminum base material by applying electrolytic graining treatment, the adhesion with the layer containing the active material is improved, and the contact area is increased by increasing the surface area, so it is suitable for current collectors. The capacity retention rate after long-term use of an electricity storage device using an aluminum base material is increased.
For the electrolytic graining treatment, for example, the conditions and apparatus described in paragraphs [0041] to [0050] of JP-A-2012-216513 can be appropriately adopted.

[Chemical etching process]
The chemical etching step is a step of removing an anodized film and a natural oxide film (hereinafter collectively referred to as an oxide film) formed on the surface of the aluminum base material. The chemical etching process removes the oxide film by chemical dissolution treatment using an alkaline aqueous solution.

The chemical etching treatment is a treatment that removes the oxide film by bringing it into contact with an alkaline aqueous solution. When an alkaline aqueous solution is brought into contact with the oxide film, the alkaline aqueous solution permeates the oxide film and dissolves the aluminum metal, thereby peeling off the oxide film. Also, the oxide film itself can be dissolved. This removes the oxide film.

Here, the anodized film is formed by forming a large number of fine uneven shapes on the bottom portion on the aluminum substrate side. Therefore, as shown in FIG. 6, a large number of fine irregularities are formed on the surface of the aluminum base material from which the anodized film has been removed.

Also, due to the chemical etching treatment and subsequent water washing treatment, aluminum hydroxide is deposited on the surface layer 4 of the aluminum base material 1 (see FIG. 4).

Examples of alkalis used in alkaline aqueous solutions include caustic alkalis and alkali metal salts. Specifically, examples of caustic alkali include sodium hydroxide (caustic soda) and caustic potash. Examples of alkali metal salts include alkali metal silicates such as sodium metasilicate, sodium silicate, potassium metasilicate and potassium silicate; alkali metal carbonates such as sodium carbonate and potassium carbonate; sodium aluminate and aluminum. alkali metal aluminates such as acid potassium; alkali metal aldonic salts such as sodium gluconate and potassium gluconate; dibasic sodium phosphate, dibasic potassium phosphate, tribasic sodium phosphate, tribasic potassium phosphate Alkali metal hydrogen phosphates may be mentioned. Among them, a solution of caustic alkali and a solution containing both caustic alkali and alkali metal aluminate are preferable from the viewpoint of high etching rate and low cost. In particular, an aqueous sodium hydroxide solution containing aluminum ions is preferred.

Here, in the production method of the present invention, by adjusting the concentration (aluminum ion concentration), temperature, and treatment time of the alkaline aqueous solution, the metal Al, Al ₂ O ₃ , Al(OH) existing within 10 nm of the surface layer ₃ , when the peak area ratios of AlO(OH) are A, B, C, and D in order, (C + D) / (A + B + C + D) is 0.5 or more and 1 or less, and C/D is 0.1 It can be set as the structure which is more than 2 or less.

The concentration of the alkaline aqueous solution is preferably 0.1-50% by mass, more preferably 0.2-10% by mass. When aluminum ions are dissolved in the alkaline aqueous solution, the concentration of aluminum ions is preferably 0.01 to 10% by mass, more preferably 0.1 to 3% by mass. The temperature of the alkaline solution is less than 50°C, preferably 25-45°C, more preferably 30-40°C. The treatment time is 10 seconds or less, preferably 1 to 8 seconds, more preferably 3 to 6 seconds.

Examples of the method of bringing the oxide film into contact with the alkaline solution include a method of passing an aluminum base material having an oxide film through a tank containing an alkaline solution, and a method of passing an aluminum base material having an oxide film through a tank containing an alkaline solution. Examples include a method of immersing the material and a method of spraying an alkaline solution onto the surface of the oxide film.

(Washing process)
A water washing step is preferably performed after the chemical etching treatment. By washing with water, the pH of the surface can be returned to neutral, and a hydroxide layer can be formed on the surface layer.

Pure water, well water, tap water, etc. can be used for washing. A nip device, an air knife, or the like may be used to prevent the processing liquid from being brought into the next step.

(Pickling process)
A pickling step is preferably performed after the chemical etching step and the water washing step.
The pickling process is a process of removing the residue 5 (see FIG. 4) generated on the surface due to the chemical etching process by washing with an acid solution.

For pickling, nitric acid, sulfuric acid, etc. can be used, and nitric acid is preferably used. An air knife, a nip device, or the like may be used to prevent the processing liquid from being brought into the next step. In particular, pickling with nitric acid is preferable because the natural oxide film formed after pickling is easily passivated.

It is preferable to carry out a water washing process similar to the above after the pickling process.

(Drying process)
A drying step may be provided after each washing step. The drying method is not limited, and known drying methods such as a method of blowing off moisture with an air knife or the like, a method of heating, and the like can be used as appropriate. Moreover, you may carry out combining several drying methods.

Ordinary aluminum base materials are rolled to a predetermined thickness. Lubricants such as rolling oil used during rolling may remain on the surface when a natural oxide film of aluminum is formed in the course of rolling. Therefore, it may be difficult to control the hydroxide within 10 nm of the surface layer using the rolled aluminum substrate as it is.

Therefore, the present inventors invented a method of removing the natural oxide film and rolling oil formed by rolling, and then controlling the hydroxide on the surface layer. As a simple method for removing the surface layer of aluminum, a method of dissolving the surface with an alkaline solution or an acid solution is known. In particular, alkaline solutions are effective in terms of production because of their excellent dissolution efficiency. However, it is difficult to stably remove the outermost surface of aluminum using an alkaline solution. This is because there are residuals such as a natural oxide film during rolling and rolling oil remaining on the outermost surface. By using an alkaline solution and taking a sufficient amount of time, it is possible to completely remove the residue on the surface layer. The inventors have discovered

Therefore, the present inventors considered using an electrochemical method as a method of removing the natural oxide film on the outermost surface formed by rolling and the remaining rolling oil. First, an anodic oxide film (anodic oxide film) is formed by causing an anodic reaction in aluminum in an acidic solution containing oxoacid. Here, the anodic oxide film is formed by changing the aluminum itself into an oxide film from the surface layer toward the inside, so the new oxide film is formed from the natural oxide film and residue (rolling oil) that originally existed on the outermost layer. Formed deep. After that, by removing the anodic oxide film, the original natural oxide film, etc. existing on the outermost layer is eliminated, and the pure aluminum inside the aluminum substrate is exposed from under the newly formed anodic oxide film. A very thin natural oxide film is formed on the surface of the exposed aluminum. In the step of removing the anodic oxide film, the formation of AlO(OH) on the surface layer is suppressed by using a very light cleaning with an alkaline solution, and Al(OH) ₃ is formed. Since Al(OH) ₃ is formed especially in the outermost layer, the interfacial resistance can be reduced even when AlO(OH) is present.

According to conventional knowledge (for example, WO18/220991), both AlO(OH) and Al(OH) ₃ are used as insulating particles to provide insulation. However, the inventors have found that the Al(OH) ₃ obtained by the above process does not easily deteriorate the resistance. Although the reason for this is not yet clear, it is presumed that most of the hydroxides formed on the surface during the above process do not exist as particles, but are present on the film in the extreme surface layer.

As a by-product of the process described above, the fine protrusions formed at the beginning of the growth of the anodic oxide film are left as fine concave shapes on the surface of the aluminum. It has been found that this is a recess having a diameter of several tens of nanometers and is formed on almost the entire surface of the aluminum surface. This fine uneven shape exhibits an effect of improving adhesion when an electrode material or the like is applied. This fine uneven shape can be quantified as a surface roughness reflecting the uneven shape by using an atomic force microscope.

It should be noted that the thickness of the anodized film formed in the film forming process should preferably be thin considering efficiency and accuracy. With regard to efficiency, this is because an excessively thick anodized film increases the load of the subsequent removal process. Regarding accuracy, if it is too thin, it will be difficult to stably expose a pure aluminum surface inside the natural oxide film and obtain a fine irregular shape at the bottom of the anodized film. In this case, it becomes necessary to prolong the chemical etching time with the alkaline solution. At this time, the dissolution of the metal aluminum further progresses in the places where the film partially dissolves quickly, and AlO ( This is because the ratio of OH) increases and becomes a disadvantageous portion for low resistance.

Also, the amount of aluminum dissolved in the chemical etching step is preferably 0.5 g/m ² or less, more preferably 0.3 g/m ² or less.

By analyzing the outermost surface of the aluminum substrate 1 by XPS, it is possible to obtain the peak area ratio of metal Al, aluminum oxide Al ₂ O ₃ , and Al hydroxide existing within 10 nm of the surface layer (see FIG. 7). ). There are two types of Al hydroxides that can be detected by this method: Al(OH) ₃ and AlO(OH). Further, by reducing the photoelectron extraction angle of XPS, it is possible to obtain more surface information. For example, by measuring at a photoelectron extraction angle of 45 degrees, information within a surface layer of 10 nm can be obtained, and by setting the photoelectron extraction angle to 20 degrees, information within a surface layer of 5 nm can be obtained.

FIG. 8 shows a schematic diagram of an example of a manufacturing apparatus for carrying out such a manufacturing method.
A manufacturing apparatus 50 shown in FIG. 8 feeds out the aluminum base material 1 from a base material roll 70 formed by winding a long aluminum base material 1, and carries out each step while conveying the aluminum base material 1 in the longitudinal direction. It is a manufacturing apparatus for manufacturing an aluminum base material for a current collector. That is, the manufacturing apparatus 50 is a manufacturing apparatus that performs each step in a roll-to-roll (RtoR) manner to manufacture an aluminum substrate for a current collector.

The manufacturing apparatus 50 includes a rotating shaft 52 loaded with a substrate roll 70, a film forming process section 56 that performs a film forming process, and a removing process section 58 that performs a removing process. and a winding shaft 54 for winding the current collector aluminum substrate 10 into a roll 72 . The film formation process section 56 and the film removal process section 58 are arranged on the path along which the aluminum base material 1 is transported from the rotating shaft 52 to the winding shaft 54 . It is desirable to place a drying device (not shown) between the removal process section 58 and the winding shaft 54 . A hot air type, a heater type, or the like can be used as the drying device.

In the manufacturing apparatus 50, feeding of the aluminum base material 1 from the base material roll 70 and winding of the current collector aluminum base material 10 on the winding shaft 54 are performed in synchronism to produce a long aluminum base material. 1 is transported in the longitudinal direction along a predetermined transport path, the aluminum substrate 1 is subjected to each of the above-described treatments in each process section. The processing performed in each process section is as described above.

It should be noted that a through-hole forming process section for performing the through-hole forming process and/or a roughening process section for performing the roughening process may be provided on the upstream side or downstream side of the film forming process section 56 . Alternatively, the coating forming process unit 56 may perform a through-hole forming process and/or a surface roughening process in addition to the coating forming process.

In addition, in the manufacturing apparatus 50, each step is performed by RtoR using the long aluminum base material 1, but it is not limited to this, and each step is performed using the sheet-shaped aluminum base material 1. You may Also, each step may be performed by a separate device.

[Current collector]
As described above, the aluminum base material for a current collector of the present invention can be used as a current collector for an electric storage device (hereinafter also referred to as "current collector").
Since the current collector has the above ratio of aluminum hydroxide, it is possible to achieve both improved adhesion to the electrode material and low resistance. Partial peeling between the electrode material (active material) and the current collector can be suppressed even when charging and discharging are performed a number of times.

<Electrode material (active material)>
The active material is not particularly limited, and known active materials used in conventional electricity storage devices can be used.
Specifically, when an aluminum base material for current collector is used as a current collector for a positive electrode, the conductive material, binder, solvent, etc. that may be contained in the active material and the active material layer are disclosed in JP-A-2003-200113. 2012-216513, paragraphs [0077] to [0088] can be employed as appropriate, the contents of which are incorporated herein by reference.
Further, when the aluminum base material for current collector is used as the current collector of the negative electrode, the material described in paragraph [0089] of JP-A-2012-216513 can be appropriately employed as the active material. The contents of which are incorporated herein by reference.

[Positive electrode]
A positive electrode using the aluminum base material for current collector of the present invention as a current collector comprises a positive electrode current collector using the aluminum base material for current collector and a positive electrode active material formed on the surface of the positive electrode current collector. A positive electrode having a layer (positive electrode active material layer) containing
Here, the positive electrode active material and the conductive material, binder, solvent, etc. that may be contained in the positive electrode active material layer are described in paragraphs [0077] to [0088] of JP-A-2012-216513. The materials described can be employed as appropriate, the contents of which are incorporated herein by reference.

[Negative electrode]
A negative electrode using the aluminum base material for current collector of the present invention as a current collector comprises a negative electrode current collector using the aluminum base material for current collector and a negative electrode active material formed on the surface of the negative electrode current collector. A negative electrode having a layer comprising:
Here, for the negative electrode active material, materials described in paragraph [0089] of JP-A-2012-216513 can be appropriately employed, the contents of which are incorporated herein by reference.

[Power storage device]
Electrodes using the aluminum substrate for current collector of the present invention as a current collector include lithium ion capacitors, electric double layer capacitors, semi-solid batteries, solid batteries, and secondary batteries using a non-aqueous electrolyte. It can be used as a positive electrode or a negative electrode of an electric storage device.
Here, regarding the specific configuration and application of the electric storage device (especially, the secondary battery), the materials and applications described in paragraphs [0090] to [0123] of JP-A-2012-216513 may be used as appropriate. can be adopted, the contents of which are incorporated herein by reference.

[Electric double layer capacitor]
An electric double layer capacitor is a capacitor having a capacitor structure of facing electrodes in which an electric double layer is used as a dielectric. An electric double layer is spontaneously generated between a solid and a liquid, and is a state in which electrons or holes are attracted to each other and aligned due to charging. A specific configuration of the electric double layer capacitor is described, for example, in Japanese Unexamined Patent Application Publication No. 2020-064971.
The aluminum substrate for current collector of the present invention can be used as a current collector for a positive electrode and/or a negative electrode of an electric double layer capacitor.

[Lithium ion capacitor]
A lithium ion capacitor uses a positive electrode of an electric double layer capacitor as a positive electrode, uses a negative electrode of a lithium ion battery as a negative electrode, and furthermore, the negative electrode is doped with lithium ions. A specific configuration of the lithium ion capacitor is described, for example, in International Publication No. 2016/084704.
The aluminum substrate for current collector of the present invention can be used as a current collector for a positive electrode and/or a negative electrode of a lithium ion capacitor.

[Solid battery]
A solid-state battery is a battery in which a solid-state electrolyte is responsible for ionic conduction between the anode and cathode. A specific configuration of the solid-state battery is described, for example, in Japanese Patent Application Laid-Open No. 2020-123538.
The current collector aluminum substrate of the present invention can be used as a current collector for a positive electrode and/or a negative electrode of a solid battery.

[Semi-solid battery]
A semi-solid battery is a battery in which a semi-solid (gel-like or clay-like) electrolyte is responsible for ionic conduction between an anode and a cathode. A specific configuration of the semi-solid battery is described in US Pat. No. 9,484,569 and the like.
The current collector aluminum substrate of the present invention can be used as a current collector for a positive electrode and/or a negative electrode of a semi-solid battery.

[Secondary battery using non-aqueous electrolyte]
A secondary battery using a non-aqueous electrolyte is a secondary battery that uses a non-aqueous electrolyte as an electrolyte between an anode and a cathode. Li-ion batteries, Na-ion batteries, K-ion batteries, or multivalent ion batteries using Mg ions, Ca ions, and the like are included. A specific configuration of a secondary battery using a non-aqueous electrolyte is described in JP-A-2017-068978 and the like.
The aluminum substrate for current collector of the present invention can be used as a current collector for a positive electrode and/or a negative electrode of a secondary battery using a non-aqueous electrolyte.

The present invention will be described in more detail below based on examples. The materials, amounts used, proportions, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed to be limited by the examples shown below.

[Preparation of aluminum substrate for current collector]
Using an aluminum substrate of alloy number 1085 or 1N30 with a thickness of 20 μm as an aluminum substrate, the following electrolytic treatment (film formation step) and removal treatment (removal step) are performed to obtain an aluminum substrate for a current collector. Current collectors A to J were produced. Current collectors A to F correspond to examples of the present invention.

<Electrolytic treatment α>
Using an aqueous solution containing 20 g/l of nitric acid and 20 g/l of sulfuric acid (liquid temperature: 50° C.), electrolytic treatment was performed using the aluminum substrate as the anode to form an anodized film on the surface of the aluminum substrate. Note that the electrolytic treatment was performed with a DC power supply. In addition, the treatment was performed by changing the amount of electric current applied in the electrolytic treatment as follows.
・The amount of electricity in the electrolytic treatment α1 is 5 C/dm ²
・The amount of electricity in the electrolytic treatment α2 is 10 C/dm ²
・The amount of electricity in the electrolytic treatment α3 is 100 C/dm ²
・The amount of electricity in the electrolytic treatment α4 is 135 C/dm ²

<Removal process β>
After the electrolysis treatment, the removal treatment was performed after washing with water. The removal treatment consists of spraying an alkaline aqueous solution (5% NaOH aqueous solution, containing 0.3-0.5% Al ions) on the surface to remove the oxide film, followed by chemical etching, followed by washing with water and nitric acid. I washed. The chemical etching process was performed by changing the conditions as follows.
・Removal treatment β1: NaOH concentration 5%, Al ion concentration 0.5%, liquid temperature 35°C, treatment time 5 seconds ・Removal treatment β2: NaOH concentration 5%, Al ion concentration 0.5%, liquid temperature 35°C, Treatment time 3 seconds Removal treatment β3: NaOH concentration 5%, Al ion concentration 0.3%, liquid temperature 37 ° C. Treatment time 5 seconds Removal treatment β4: NaOH concentration 5%, Al ion concentration 0.3%, liquid Temperature 37°C, processing time 40 seconds

Table 1 shows the treatment conditions for the aluminum base material for each current collector. In addition, the current collector G is an untreated aluminum base material. That is, it is an aluminum base material having a natural oxide film on its surface formed during rolling. The current collector J is an aluminum substrate having an undercoat layer formed by applying conductive carbon particles together with a binder to the surface of an untreated aluminum substrate and drying the resultant.

The number of intermetallic compounds in the aluminum substrate was 460/mm ² for the 1085 material and 7800/mm ² for the 1N30 material.

After the production of each aluminum base material for current collector, the peak area ratio of aluminum hydroxide present within a depth of 10 nm from the surface layer was examined using XPS. This measurement was not performed for current collector J because the carbon conductive material and the binder were applied in advance to the entire surface of the aluminum base material.

The measurement conditions by XPS are as follows.
・Apparatus: Quantera SXM manufactured by Ulvac-PHI
・X-ray source: Al Kα ray (1486.6 ev, 25 W, 15 kv)
・Pass Energy = 55 ev, Step = 0.05 ev
・Measurement area: 300 μm × 300 μm
- Fitting was performed after performing peak shift correction on the obtained Al2P spectrum based on the peak position of metal Al.
・Peak area ratio: Peak areas for a total of four types of metal Al, aluminum oxide Al ₂ O ₃ , aluminum hydroxide Al (OH) ₃ , and boehmite AlO (OH) for which peaks were obtained after performing the above fitting I asked for a ratio.
Photoelectron extraction angle: 45 degrees Table 2 shows the results of XPS analysis performed at a photoelectron extraction angle of 45 degrees. Current collectors A, B, C, D, E, and F having a peak area ratio of Al(OH) ₃ /AlO(OH)=C/D of 0.1 or more and 1 or less are examples. Three of G, H, and I are comparative examples.

Similarly, Table 3 shows the results of XPS analysis with a photoelectron extraction angle of 20 degrees. This is the peak area ratio of aluminum hydroxide existing within 5 nm in depth from the surface layer.

Since current collector G was an untreated aluminum substrate, Al ₂ O ₃ formed immediately after rolling was detected, but hydroxide was not detected.

[Examples 1 to 6, Comparative Examples 1 to 4]
Adhesion and resistance were evaluated using the produced aluminum substrates for current collectors (current collectors A to J) as Examples 1 to 6 and Comparative Examples 1 to 4, respectively.

<Resistance>
A carbon material (Bunny Height T602 manufactured by Nippon Graphite Co., Ltd.) was applied as an electrode material layer to an aluminum substrate for a current collector so that the dry coating thickness was 10 μm, and as shown in FIG. 9, an electrode material layer 106 was formed. The aluminum base material for an electric body was sandwiched between a pressurized conductive terminal and a pressurized insulating terminal, and the resistance was measured with a resistance measuring machine (HIOKI 3541 manufactured by Hioki Co., Ltd.) with N=7 samples. The distance between the measurement terminals was fixed at 50 mm.

The initial resistance evaluation was performed after storing in the DRYBOX for 24 hours or more before evaluation.

Next, forced aging resistance evaluation was performed. Each aluminum base material for a current collector was stored in an environment with a temperature of 30° C. and a humidity of 80%. Two weeks later, an electrode material layer was formed by the method described above, and resistance was evaluated. Similarly, after storage for 4 weeks at a temperature of 30° C. and a humidity of 80%, an electrode material layer was formed by the method described above, and resistance was evaluated.
Table 4 shows the results.

As shown in Table 4, Examples 1 to 6 of the present application are superior to Comparative Examples 1 and 2 in that the resistance values are small from the initial stage to after high-humidity storage.
In addition, since Example 6 uses an aluminum base material containing a large amount of intermetallic compounds, it can be seen that deterioration in resistance after high-humidity storage is less than other examples, and is superior.
Comparative Example 3 has a lower initial resistance than the Examples, but the range of deterioration in resistance after high-humidity storage is better than the other Comparative Examples because it uses an aluminum base material containing a large amount of intermetallic compounds.
Comparative Example 4 is a substrate undercoated with conductive carbon, and the initial resistance and the resistance up to 2 weeks after high humidity storage are excellent as in Examples, but the resistance value increases after 4 weeks of high humidity storage. rice field. The cause of this is not clear, but it is presumed that the resistance deteriorated due to changes such as bleeding of the binder for fixing the undercoat material.

Next, the surface shape of each aluminum substrate for current collector was observed.
10 is a surface SEM image of Example 3, and FIGS. 11 and 12 are surface SEM images of Comparative Example 1 and Comparative Example 2, respectively. From FIG. 10, it can be seen that the surface of the aluminum base material for current collector of Example 3 has a fine uneven structure on the order of several tens of nanometers. On the other hand, it can be seen that such a structure is not formed in the current collector aluminum substrates of Comparative Examples 1 and 2.

For the current collector aluminum substrates (current collectors A to I) of each example and comparative example, physical property values representing the shape of the surface were obtained using an atomic force microscope (AFM). Table 5 shows the results obtained by measuring the surface shape of 1 μm square and obtaining the surface physical property values from the obtained three-dimensional data.

The measurement conditions for the atomic force microscope are as follows.
・Measurement area: 1 μm × 1 μm
・Equipment: Hitachi High-Tech Science AFM5100N type SPM (used in tapping mode)
・ Cantilever: OMCL-AC200TS-R3 manufactured by Olympus
・Resolution: 256 x 256 pixels

The following two physical property values were obtained from the obtained three-dimensional data.
・Average surface roughness:

(Zc is the Z coordinate of the central plane (height direction))
・Maximum height difference: PV (nm): maximum value - minimum value of Z coordinate in the measurement plane. The surface roughness Ra and the maximum height difference PV were also obtained by a method of removing irregularities with a period exceeding 0.2 μm by processing.
The results are shown in Table 5 together. In Table 5, the surface roughness Ra and the maximum height difference PV obtained by the method of removing irregularities with a period exceeding 0.2 μm by performing FFT processing are indicated as “with FFT processing”.

Since the current collectors A to F of Examples 1 to 6 have fine irregularities on the surface, when measured with an atomic force microscope under the above measurement conditions, the average surface reflecting the irregularities Roughness is measured. Since the current collector G of Comparative Example 1 is an aluminum foil that is not surface-treated, Ra is small. In the current collector H of Comparative Example 2, since the anodized film was partially left on the surface, fine unevenness remained only partially, and Ra was a small value. Since there is a difference in the presence or absence of an oxide film, the maximum height difference: PV was a relatively large value. Since current collector I of Comparative Example 3 had a large amount of dissolution in the alkaline solution, no fine irregularities remained, and Ra was a small value. However, as shown in FIG. 12, since the undulation component exists on the surface, the maximum height difference: PV has a relatively large value. In the FFT-processed data, the difference between the example and the comparative example was particularly clear in the PV value.

<Adhesion>
In order to evaluate the adhesion strength of the aluminum substrates for current collectors of Examples and Comparative Examples, two types of evaluation were performed.

<<Adhesion evaluation 1>>
On the surface of each of the aluminum substrates for current collectors of Examples 1 to 6 and Comparative Examples 1 to 3, an adhesive tape (tape "PS1" manufactured by JTS Co., Ltd.: width 25 mm) 158 for peeling test was applied. Directly pasted, each aluminum base material S for current collector is fixed to the pasting table 154 on the slide table 152 for 90 degree peeling test with the surface facing up with double-sided tape 156, and the pasted adhesive tape 158 is peeled off. It was carried out by a method of measuring the load at the time. The peel strength was evaluated using a peel tester 162 manufactured by Imada Co., Ltd., and the maximum force (N/25 mm) during peeling was evaluated. FIG. 13 shows a schematic diagram of a peel test evaluation apparatus.

<<Adhesion evaluation 2>>
An electrode material kneaded with 95% activated carbon, 4% water, and 0.5% CMC was applied to a thickness of about 15 μm on the surface of each of the aluminum substrates for current collectors of Examples 1 to 6 and Comparative Examples 1 to 3, After drying the electrode material, the aluminum base material for the current collector was cut to 100 mm × 20 mm, wound around a stainless steel round bar with a diameter of 20 mm so that the electrode material was on the outside, and unwound. The state of peeling from the material was visually observed and evaluated according to the following criteria.
・A: No delamination occurred at the interface between the electrode material and the aluminum substrate for the current collector ・B: Delamination occurred at 1 to 2 locations ・C: Delamination occurred at 3 or more locations Table 6 shown in

From Table 6, it can be seen that the examples of the present application have higher adhesion than the comparative examples, and peeling after application of the electrode material is less likely to occur. In the examples, the surface microstructure is believed to be effective for adhesion.

From the above results, it can be seen that the examples of the present invention can achieve both high adhesion and low resistance compared to the comparative examples.
From the above, the effect of the present invention is clear.

1 aluminum base material 2 natural oxide film 3 anodized film 4 surface layer portion where aluminum hydroxide is deposited 5 residue 50 manufacturing apparatus 52 rotating shaft 54 winding shaft 58 removing process unit 70 base roll 72 roll 74 chemical etching process unit 76 washing with water Process part 78 Pickling process part 80 Water washing process part 100 Resistance measuring device 102 Pressurized conductive dedicated terminal 104 Pressurized insulated terminal 106 Active material layer 150 Slide rail 152 Slide table 154 Attachment table 156 Double-sided tape 158 Adhesive tape 160 Clamp 162 Digital Force gauge 164 Tensile device S Sample for evaluation

Claims

A, B, C, and D represent peak area ratios of metal Al, Al2O3 , Al(OH) 3 , and AlO(OH) present within 10 nm of the surface layer when measured by X-ray photoelectron spectroscopy. and (C+D)/(A+B+C+D) is 0.5 or more and 1 or less, and C/D is 0.1 or more and 2 or less.
The aluminum substrate for current collector according to claim 1, wherein the surface roughness Ra of the surface is 10 nm or more and 50 nm or less.
3. The aluminum base material for a current collector according to claim 1, wherein the maximum height difference PV of the surface is 100 nm or more and 500 nm or less.
The aluminum substrate for a current collector according to any one of claims 1 to 3, wherein the surface has a granular intermetallic compound.
The aluminum substrate for current collector according to claim 4, wherein the number density of the particulate metal compound is 500/ mm2 or more.
The aluminum substrate for current collector according to any one of claims 1 to 5, which has a thickness of 5 µm to 100 µm.
A capacitor comprising the aluminum substrate for current collector according to any one of claims 1 to 6.
A secondary battery comprising the aluminum substrate for current collector according to any one of claims 1 to 6.
A method for producing an aluminum substrate for a current collector for producing the aluminum substrate for a current collector according to any one of claims 1 to 6,
a film-forming step of forming an anodized film on the surface of the aluminum foil at a current of 10 to 100 C/dm 2 during anodic electrolysis;
A method for producing an aluminum base material for a current collector, comprising a removing step of removing the anodized film.
The method for producing an aluminum base material for a current collector according to claim 9, wherein the removal step includes, in this order, a chemical etching step with an alkaline solution, a water washing step, a washing step with an acid solution, and a water washing step.
The method for producing an aluminum substrate for a current collector according to claim 10, wherein the chemical etching step includes a step of contacting the anodized film with an alkaline solution at 25°C or higher and lower than 50°C for 1 to 10 seconds.